Method and system for identifying power system element parameters and power correction factor

ABSTRACT

The invention discloses a method and system for identifying an element parameter and a power correction factor of an electric power system. The method comprises: inputting an active power telemetering steady state value {circumflex over (P)}, a reactive power telemetering steady state value {circumflex over (Q)}, and a voltage telemetering state value Û of a power grid with n elements, to establish  P +j Q ={circumflex over (P)}+j{circumflex over (Q)}+G(β, {circumflex over (P)}, {circumflex over (Q)}) for telemetering power, where G(β, {circumflex over (P)}, {circumflex over (Q)}) is power correction function regarding {circumflex over (P)} and {circumflex over (Q)}, and β is power correction factor; establishing F(Y, P , Q ,Û)= 0 , where Y is an admittance matrix of the n elements; setting F(Y, P , Q ,Û)=ε and J=ε T ·ε, minimizing J, and determining Y and β; restoring element parameters including resistance R, reactance X and susceptance B from Y; and outputting R,X,B and β. The method can identify element parameters and power correction factor with high identification accuracy improve qualified rate of state estimation and improve accuracy of applications such as stability analysis, stability checking and stability control, etc.

FIELD OF THE INVENTION

The present invention relates to an automation technology of a power grid scheduling, and in particular, to a method and system for identifying element parameters and a power correction factor of an electric power system.

BACKGROUND OF THE INVENTION

An element parameter identification of an electric power system can provide data basis for data processing, computation analysis, online tests, fault diagnosis, working condition prediction, etc. of the electric power system and play an important role in increasing analysis and computation for an electric power system.

According to current element parameter method, the obtained element parameters are with large errors, and especially, the parameters of an electric transmission line are with relatively large errors. The actual measurement error can be above 30%, and the theoretical parameter error of IEEE is also around 20%. It seriously impacts the computational accuracy of programs such as state estimations, stability analysis, etc. of an electric power system, and may even cause wrong judgments.

In the patent “Data sampling method and system, as well as method and system applying the data sampling method and system to parameter identification”(CN Application No. CN201210408534.9), the obtained sample sequence undergo a steady state processing after undergoing low-pass filtering and re-sampling, and then static parameters of the system are identified. Such method for identifying an element parameter of an electric power system is impacted by measurement errors, especially impacted by a current transformer (CT) error and a potential transformer (PT) error, causing deviation of the identified element parameters.

SUMMARY OF THE INVENTION

In order to solve an aforementioned technical problem, the present invention provides a method for identifying an element parameter and a power correction factor of an electric power system, comprising the following steps:

-   -   S1: inputting an active power telemetering steady state value         {circumflex over (P)}, a reactive power telemetering steady         state value {circumflex over (Q)}, and a voltage telemetering         steady state value Û of a power grid with n elements,         comprising:     -   if n=1, inputting an active power telemetering steady state         value {circumflex over (P)}_(c), a reactive power telemetering         steady state value {circumflex over (Q)}_(c), and a voltage         telemetering state value Û_(c) corresponding to the element; if         n>1, inputting an active power telemetering steady state value         {circumflex over (P)}_(c), a reactive power telemetering steady         state value {circumflex over (Q)}_(c), and a voltage         telemetering steady state value Û_(c) corresponding to each         element, and inputting an active power telemetering steady state         value {circumflex over (P)}_(i) and a reactive power         telemetering steady state value {circumflex over (Q)}_(i)         injected to a power grid node, where i=1,2, . . . ,N, and N is         the number of the power grid nodes;     -   S2: establishing a power correction equation P+jQ={circumflex         over (P)}+j{circumflex over (Q)}+G(β, {circumflex over (P)},         {circumflex over (Q)}) for a telemetering power, where G(β,         {circumflex over (P)}, {circumflex over (Q)}) is a power         correction function regarding {circumflex over (P)} and         {circumflex over (Q)}, β is a power correction factor, P is an         active power telemetering correction value and Q is a reactive         power telemetering correction value;     -   S3: establishing a power voltage equation F(Y,P,Q,Û)=0, where Y         is an admittance matrix related to said n elements; if n=1, said         power voltage equation comprises a power voltage equation of an         element; if n>1, said power voltage equation comprises a power         voltage equation of an element and a power voltage equation of         the power grid node;     -   S4: setting F(Y,P,Q,Û)=ε, J=ε^(T)·ε, where ε^(T) is a transposed         vector of ε; establishing simultaneous equations with         P+jQ={circumflex over (P)}+j{circumflex over (Q)}+G(β,         {circumflex over (P)}, {circumflex over (Q)}), minimizing J and         determining Y and β;     -   S5: restoring element parameters including resistance R,         reactance X and susceptance B;     -   S6: outputting the element parameters R,X,B and the power         correction factor β.

Wherein, G(β, {circumflex over (P)}, {circumflex over (Q)})=β_(p1)·{circumflex over (P)}+β_(p2)·{circumflex over (Q)}+β_(p0)+j(β_(q1)·{circumflex over (P)}+β_(q2)·{circumflex over (Q)}+β_(q0)), and β={β_(p1), β_(p2), β_(p0), β_(q1), β_(q2), β_(q0)}.

Wherein, G(β, {circumflex over (P)}, {circumflex over (Q)})=β·({circumflex over (P)}+j{circumflex over (Q)}), β=β_(r)+jβ_(m).

Wherein, said minimizing J and determining Y and β comprise conducting value-estimating for Y and β according to the theory of linear optimization or the theory of nonlinear optimization, so as to make J obtain a minimum value.

Wherein, said active power telemetering steady state value {circumflex over (P)}, reactive power telemetering steady state value {circumflex over (Q)} and voltage telemetering steady state value Û of a power grid with n elements are obtained according to the following steps: P1, inputting telemetering values of the electric power grid; P2, conducting steady state processing on the telemetering values and obtaining telemetering steady state values; P3, selecting said active power telemetering steady state value {circumflex over (P)}, reactive power telemetering steady state value {circumflex over (Q)} and voltage telemetering steady state value Û of the power grid with n elements from the telemetering steady state values, that are an active power telemetering steady state value {circumflex over (P)}_(c), a reactive power telemetering steady state value {circumflex over (Q)}_(c), and a voltage telemetering steady state value Û_(c) of each element, and an active power telemetering steady state value {circumflex over (P)}_(i) and a reactive power telemetering steady state value {circumflex over (Q)}_(i) injected to a power grid node, where i=1,2, . . . ,N, and N is the number of the power grid nodes.

Wherein, for F(Y, P, Q, Ū):

-   -   If n=1 ,     -   F(Y,P,Q,Ū)=P _(c)+jQ _(c)−Û_(c)·*({tilde over (Y)}·Ũ_(c)) ,         where Y is an admittance matrix of an element;     -   if n>1,

${F\left( {Y,\overset{\_}{P},\overset{\_}{Q},\hat{U}} \right)} = \left\{ \begin{matrix} {{\overset{\_}{P}}_{c} + {j{\overset{\_}{Q}}_{c}} - {{\hat{U}}_{c} \cdot^{*}\left( {\overset{\sim}{Y} \cdot {\overset{\sim}{U}}_{c}} \right)}} & {{power}\mspace{14mu} {voltage}\mspace{14mu} {equation}\mspace{14mu} {of}\mspace{14mu} {element}} \\ {{{\overset{\_}{P}}_{i} + {j{\overset{\_}{Q}}_{i}} - {\sum\limits_{k = 1}^{n_{i}}\; \left( {{\overset{\_}{P}}_{ik} + {j{\overset{\_}{Q}}_{ik}}} \right)}},{i = 1},2,\ldots,N,} & {{power}\mspace{14mu} {voltage}\mspace{14mu} {equation}\mspace{14mu} {of}\mspace{14mu} {power}\mspace{14mu} {grid}\mspace{14mu} {node}} \end{matrix} \right.$

Where Y is an admittance matrix related ton elements, {tilde over (Y)} is a conjugate matrix of Y, Ũ_(c) is a conjugation of Û_(c), “·*” stands for multiplying the corresponding items; n_(i) is the number of elements connected to node i, P _(ik) is an active power telemetering correction value of element k connected to node i, Q _(ik) is a reactive power telemetering correction value of element k connected to node i.

Correspondingly, the present invention provides further a system for identifying an element parameter and a power correction factor of an electric power system, comprising the following units:

-   -   a steady state value input unit, used for inputting an active         power telemetering steady state value {circumflex over (P)}, a         reactive power telemetering steady state value {circumflex over         (Q)} and a voltage telemetering steady state value Û of a power         grid with n elements, comprising: if n=1, inputting an active         power telemetering steady state value {circumflex over (P)}_(c),         a reactive power telemetering steady state value {circumflex         over (Q)}_(c) and a voltage telemetering steady state value         Û_(c) corresponding to the element; if n>1, inputting an active         power telemetering steady state value {circumflex over (P)}_(c),         a reactive power telemetering steady state value {circumflex         over (Q)}_(c) and a voltage telemetering steady state value         Û_(c) corresponding to each element, and inputting an active         power telemetering steady state value {circumflex over (P)}_(i)         and a reactive power telemetering steady state value {circumflex         over (Q)}_(i) injected to a power grid node, where n≧1,i=1,2, .         . . ,N and N is the number of the power grid nodes;     -   a minimal calculating unit, used for establishing a power         correction equation P+jQ={circumflex over (P)}+j{circumflex over         (Q)}+G(β,{circumflex over (P)},{circumflex over (Q)}) for a         telemetering power, where G(β,{circumflex over (P)},{circumflex         over (Q)}) is a power correction function regarding {circumflex         over (P)} and {circumflex over (Q)}, β is a power correction         factor, P is an active power telemetering correction value and Q         is a reactive power telemetering correction value; establishing         a power voltage equation F(Y,P,Q,Û)=0, where Y is an admittance         matrix related to said n elements; if n=1, said power voltage         equation comprises a power voltage equation of an element; if         n>1, said power voltage equation comprises a power voltage         equation of an element and a power voltage equation of the power         grid; setting F(Y,P,Q,Û)=ε, J=ε^(T)·ε, where ε^(T) is a         transposed vector of ε; establishing simultaneous equations with         P+jQ={circumflex over (P)}+j{circumflex over         (Q)}+G(β,{circumflex over (P)},{circumflex over (Q)}),         minimizing J and determining Y and β;     -   a restoring unit, used for restoring element parameters         including resistance R, reactance X and susceptance B from Y;     -   an output unit, used for outputting the element parameters R, X,         B and the power correction factor β.

Wherein, G(β,{circumflex over (P)},{circumflex over (Q)})=β_(p1)·{circumflex over (P)}+β_(p2)·{circumflex over (Q)}+β_(p0)+j(β_(q1)·{circumflex over (P)}+β_(q2)·{circumflex over (Q)}+β_(q0)), and β={β_(p1), β_(p2), β_(p0), β_(q1), β_(q2), β_(q0)}.

Wherein, G(β,{circumflex over (P)},{circumflex over (Q)})=β·({circumflex over (P)}+j{circumflex over (Q)}), β=β_(r)+jβ_(m).

Further, the system also comprises a steady-state value acquisition unit, and said steady-state value acquisition unit comprises: a steady-state processing module, used for conducting steady-state processing on telemetering values of the electric power system and obtaining telemetering steady state values; a steady-state value selection module, used for selecting said active power telemetering steady state value {circumflex over (P)}, reactive power telemetering steady state value {circumflex over (Q)} and voltage telemetering steady state value Û of the power grid with n elements from the telemetering steady state values.

Wherein for F(Y,P,Q,Û),

-   -   if n=1,     -   F(Y,P,Q,Û)=P _(c)+jQ _(c)−Û_(c)·*({tilde over (Y)},Ũ_(c)), where         Y is an admittance matrix of an element;     -   if n>1,

${F\left( {Y,\overset{\_}{P},\overset{\_}{Q},\hat{U}} \right)} = \left\{ \begin{matrix} {{\overset{\_}{P}}_{c} + {j{\overset{\_}{Q}}_{c}} - {{\hat{U}}_{c} \cdot^{*}\left( {\overset{\sim}{Y} \cdot {\overset{\sim}{U}}_{c}} \right)}} & {{power}\mspace{14mu} {voltage}\mspace{14mu} {equation}\mspace{14mu} {of}\mspace{14mu} {element}} \\ {{{\overset{\_}{P}}_{i} + {j{\overset{\_}{Q}}_{i}} - {\sum\limits_{k = 1}^{n_{i}}\; \left( {{\overset{\_}{P}}_{ik} + {j{\overset{\_}{Q}}_{ik}}} \right)}},{i = 1},2,\ldots,N,} & {{power}\mspace{14mu} {voltage}\mspace{14mu} {equation}\mspace{14mu} {of}\mspace{14mu} {power}\mspace{14mu} {grid}\mspace{14mu} {node}} \end{matrix} \right.$

-   -   where Y is an admittance matrix related to n elements, {tilde         over (Y)} is a conjugate matrix of Y, Ũ_(c)is a conjugation of         Û_(c), “·*” stands for multiplying the corresponding items;         n_(i) is the number of elements connected to node i , P _(ik) is         an active power telemetering correction value of element k         connected to node i, and Q _(ik) is a reactive power         telemetering correction value of element k connected to node i.

The identified power correction factor β in the present invention can be used for online correcting for an telemetering active power value and an telemetering reactive power value, the β obtained by identification has already reckoned in influences of current transformer (CT) errors, potential transformer (PT) errors and reactive measurement formula, so that it is not necessary to further consider the reactive measurement errors. Moreover, the present invention also identifies an element parameters as well, substituting the element parameters into online application equations, under coaction of the power correction factor β and the element parameters, the pass rate of state estimation and application precision such as stability analysis, stability check and stability control, etc. can be improved.

BRIEF DISCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a method for identifying an element parameters and a power correction factor of an electric power system according to the present invention;

FIG. 2 is a block diagram of a system for identifying an element parameters and a power correction factor of an electric power system according to the present invention;

FIG. 3 (a) is a circuit diagram of a CT;

FIG. 3 (b) is an equivalent circuit diagram of a CT;

FIG. 4 is an equivalent circuit diagram of an electric transmission line;

FIG. 5 is equivalent circuit diagram of a three-winding transformer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments of the present invention will now be described in detail with reference to the drawings.

Referring to FIG. 1, the method for identifying an element parameters and a power correction factor of an electric power system according to the present invention comprises the following steps in sequence:

-   -   (1) inputting telemetering values of an electric power grid;     -   (2) conducting steady state processing on the telemetering         values, and obtaining telemetering steady state values;     -   (3) selecting said active power telemetering steady state value         {circumflex over (P)}, reactive power telemetering steady state         value {circumflex over (Q)} and voltage telemetering steady         state value Û of the power grid with n elements from the         telemetering steady state values;     -   (4) establishing a power correction equation P+jQ={circumflex         over (P)}+j{circumflex over (Q)}+G(β,{circumflex over         (P)},{circumflex over (Q)}) for a telemetering power, where         G(β,{circumflex over (P)},{circumflex over (Q)}) is a power         correction function regarding {circumflex over (P)} and         {circumflex over (Q)}, β is a power correction factor, P is an         active power telemetering correction value and Q is a reactive         power telemetering correction value;     -   (5) establishing a power voltage equation F(Y,P,Q,Û)=0, where Y         is an admittance matrix related to said n elements;     -   (6) setting F(Y,P,Q,Û)=ε, J=ε^(T)·ε, where ε^(T) is a transposed         vector of ε; establishing simultaneouse quations with         P+jQ={circumflex over (P)}+j{circumflex over (Q)}+G(β,         {circumflex over (P)}, {circumflex over (Q)}), minimizing J and         determining Y and β;     -   (7) restoring element parameters including resistance R,         reactance X and susceptance B from Y;     -   (8)outputting the element parameters R,X,B and the power         correction factor β.

Wherein, the telemetering values inputted to the electric power grid are obtained from an electric SCADA (Supervisory Control and Data Acquisition) system or are historical telemetering values of the SCADA.

Wherein, one person skilled in the art may conceive of various methods for said steady state processing or refer to CN Patents No.201210407925.9 or No.201210408535.3.

Wherein, G(β,{circumflex over (P)},{circumflex over (Q)})=β_(p1)·{circumflex over (P)}+β_(q2)·{circumflex over (Q)}+β_(p0)+j(β_(q1)·{circumflex over (P)}+β_(q2)·{circumflex over (Q)}+β_(q0)) and β={β_(p1), β_(p2), β_(p0), β_(q1), β_(q2), β_(q0)}.

With further simplification, G(β,{circumflex over (P)},{circumflex over (Q)})=β·({circumflex over (P)}+j{circumflex over (Q)}) and β=β_(r)+jβ_(m).

Wherein, said minimizing J and determining Y and β is to obtain the admittance matrix Y and the power correction factor β according to an optimization method, specifically, by firstly substituting P+jQ={circumflex over (P)}+j{circumflex over (Q)}+G(β,{circumflex over (P)},{circumflex over (Q)}) into F(Y,P,Q,Û)=0, setting F(Y,P,Q,Û)=ε, J=ε^(T)·ε, then conducting value-estimating for Y and β, making J obtain a minimum value according to the theory of linear optimization or the theory of nonlinear optimization.

Referring to FIG. 3(a) and 3(b), for a current transformer CT, Z_(o) is an equivalent internal impedance of the CT, Z_(L) is an equivalent load of a secondary circuit of the CT,

${{\overset{.}{I}}_{2}^{\prime} = {\frac{Z_{O}}{Z_{O} + Z_{L}} \cdot {\overset{.}{I}}_{2}}},$

so

${{\overset{.}{I}}_{2} = {\left( {1 + \frac{Z_{L}}{Z_{O}}} \right) \cdot {\overset{.}{I}}_{2}^{\prime}}},$

substituting it into formula S of an apparent power:

$S = {{P + {jQ}} = {{{\overset{.}{U}}_{2} \cdot {\overset{\sim}{I}}_{2}} = {{\overset{.}{U}}_{1} \cdot {\overset{\sim}{I}}_{2}^{\prime} \cdot {\left( {1 + \frac{Z_{L}^{\sim}}{Z_{O}^{\sim}}} \right).}}}}$

It can be seen, for the current transformer, the power error can be reflected by P+jQ=P′+jQ′+β·(P′+jQ′), where β is a power correction factor.

If only single element needs to be identified, that is, n=1:

-   -   said {circumflex over (P)}, {circumflex over (Q)} and Û         comprise: an active power telemetering steady state value         {circumflex over (P)}_(c), a reactive power telemetering steady         state value {circumflex over (Q)}_(c) and a voltage telemetering         steady state value Û_(c) corresponding to the element, for         example: (a)for one line, an active power telemetering steady         state value {circumflex over (P)}_(c), a reactive power         telemetering steady state value {circumflex over (Q)}_(c) and a         voltage telemetering steady state value Û_(c) of two terminals         of the line needs to be selected; (b) for a two-winding         transformer, an active power telemetering steady state value         {circumflex over (P)}_(c), a reactive power telemetering steady         state value {circumflex over (Q)}_(c) and a voltage telemetering         steady state value Û_(c) of two terminals of the two-winding         transformer shall be selected; (c) for a three-winding         transformer, an active power telemetering steady state value         {circumflex over (P)}_(c), a reactive power telemetering steady         state value {circumflex over (Q)}_(c) and a voltage telemetering         steady state value Û_(c) of three terminals of the three-winding         transformer shall be selected. As can be seen, for any element         of the present invention, {circumflex over (P)}_(c), or         {circumflex over (Q)}_(c) or Û_(c) comprises M values, where         M=α·L, L is group number of the telemetering steady state         values, if the element is a two-port element, α=2, if the         element is a three-port element, α=3.

A power voltage equation of single element can be written as P _(c)+jQ _(c)−Û_(c)·*({tilde over (Y)}·Ũ)=0, F(Y,P,Q,Û)=P _(c)+jQ _(c)−Û_(c)·.*({tilde over (Y)}·Ũ_(c)).

The admittance matrix Y of the element can be obtained by minimizing, and then the element parameters R, X, B can be restored through the relationship between the element admittance and the element parameters R,X,B.

If multiple elements need to be identified, that is, n>1:

-   -   said {circumflex over (P)}, {circumflex over (Q)} and Û         comprise: an active power telemetering steady state value         {circumflex over (P)}_(c), a reactive power telemetering steady         state value {circumflex over (Q)}_(c) and a voltage telemetering         steady state value Û_(c) corresponding to each element, and an         active power telemetering steady state value {circumflex over         (P)}_(i) and a reactive power telemetering steady state value         {circumflex over (Q)}_(i) injected to a power grid node, where         i=1,2, . . . ,N and N is the number of the power grid nodes;     -   for a power grid connected by multiple elements: conducting         ranking for multiple power voltage equations of single element,         wherein the final obtained power equation of the element is just         like a single element in formality, diagonal elements of the         block matrix of Y is the admittance matrix of single element;         meanwhile, the power equation of each node in the power grid         meets the power equation of the node, an injection power equals         to an outflow power

${{P_{i} + {jQ}_{i} - {\sum\limits_{k = 1}^{n_{i}}\; \left( {P_{ik} + {jQ}_{ik}} \right)}} = 0},$

k=1,2, . . . ,N, where P_(i) is an active power injected to node i, Q_(i) is a reactive power injected to node i, n_(i) is the number of elements connected to node i, P_(ik) is an active power telemetering correction value of element No. k connected to node i, Q_(ik) is a reactive power telemetering correction value of element No. k connected to node i, and N is the node number of a power grid.

As can be seen, for a power grid formed from multiple elements, after conducting power correction for the telemetering steady state value according to P+jQ={circumflex over (P)}+j{circumflex over (Q)}+G(β,{circumflex over (P)},{circumflex over (Q)}), substituting an element power equation and an power-flow equation can both meet

${{{\overset{\_}{P}}_{i} + {j{\overset{\_}{Q}}_{i}} - {\sum\limits_{k = 1}^{n_{i}}\; \left( {{\overset{\_}{P}}_{ik} + {j{\overset{\_}{Q}}_{ik}}} \right)}} = 0},$

so

${F\left( {Y,\overset{\_}{P},\overset{\_}{Q},\hat{U}} \right)} = \left\{ \begin{matrix} {{\overset{\_}{P}}_{c} + {j{\overset{\_}{Q}}_{c}} - {{\hat{U}}_{c} \cdot^{*}\left( {\overset{\sim}{Y} \cdot {\overset{\sim}{U}}_{c}} \right)}} & {{power}\mspace{14mu} {voltage}\mspace{14mu} {equation}\mspace{14mu} {of}\mspace{14mu} {element}} \\ {{{\overset{\_}{P}}_{i} + {j{\overset{\_}{Q}}_{i}} - {\sum\limits_{k = 1}^{n_{i}}\; \left( {{\overset{\_}{P}}_{ik} + {j{\overset{\_}{Q}}_{ik}}} \right)}},{i = 1},2,\ldots,N,} & {{power}\mspace{14mu} {voltage}\mspace{14mu} {equation}\mspace{14mu} {of}\mspace{14mu} {power}\mspace{14mu} {grid}\mspace{14mu} {node}} \end{matrix} \right.$

Where Y is an admittance matrix related to n elements, {tilde over (Y)} is a conjugate matrix of Y, Ũ_(c) is a conjugation of Û_(c), “·*” stands for multiplying the corresponding items; n_(i) is the number of elements connected to node i, P _(ik) is an active power telemetering correction value of element No. k connected to node i, and Q _(ik) is a reactive power telemetering correction value of element No. k connected to node i, and N is the node number of a power grid.

After obtaining the admittance matrix Y by minimizing, the elements parameters can be restored from the admittance matrix Y. Firstly the admittance matrix of each element is restored from Y, and then the element parameters R,X,B are restored through the relationship between the admittance matrix of each element and the element parameters R,X,B.

Referring to FIG. 2, FIG. 2 is a block diagram of a system for identifying an element parameters and a power correction factor of an electric power system according to the present invention, comprising:

-   -   a steady-state value acquisition unit (1), comprising a         steady-state processing module (11) and a steady-state value         selection module (12) :said steady-state processing module (11)         is used for conducting steady-state processing on telemetering         values of the electric power system and obtaining telemetering         steady state values; said steady-state value selection module         (12) is used for selecting said active power telemetering steady         state value {circumflex over (P)}, reactive power telemetering         steady state value {circumflex over (Q)} and voltage         telemetering steady state value Û of the power grid with n         elements from the telemetering steady state values; if n=1, said         {circumflex over (P)}, {circumflex over (Q)} and Û comprise an         active power telemetering steady state value {circumflex over         (P)}_(c), a reactive power telemetering steady state value         {circumflex over (Q)}_(c) and a voltage telemetering state value         Û_(c), corresponding to the element; if n>1, said {circumflex         over (P)}, {circumflex over (Q)} and Û comprise an active power         telemetering steady state value {circumflex over (P)}_(c), a         reactive power telemetering steady state value {circumflex over         (Q)}_(c) and a voltage telemetering steady state value Û_(c)         corresponding to each element, and an active power telemetering         steady state value {circumflex over (P)}_(i) and a reactive         power telemetering steady state value {circumflex over (Q)}_(c)         injected to a power grid node, where i=1,2, . . . ,N, and N is         the number of the power grid nodes;     -   a minimal calculating unit (2), used for establishing a power         correction equation P+jQ={circumflex over (P)}+j{circumflex over         (Q)}+G(β,{circumflex over (P)},{circumflex over (Q)}) for a         telemetering power, where G(β,{circumflex over (P)},{circumflex         over (Q)}) is a power correction function regarding {circumflex         over (P)} and {circumflex over (Q)}, β is a power correction         factor, P is an active power telemetering correction value and Q         is a reactive power telemetering correction value; establishing         a power voltage equation F(Y,P,Q,Û)=0, where Y is an admittance         matrix related to said n elements; if n=1, said power voltage         equation comprises a power voltage equation of an element P         _(c)+jQ _(c)−Û_(c)·*({tilde over (Y)}·Ũ_(c))=0; if n>1, said         power voltage equation comprises a power voltage equation of an         element P _(c)+jQ _(c)−Û_(c)·*({tilde over (Y)}·Ũ_(c))=0 and a         power voltage equation of the power grid

${{{\overset{\_}{P}}_{i} + {j{\overset{\_}{Q}}_{i}} - {\sum\limits_{k = 1}^{n_{i}}\; \left( {{\overset{\_}{P}}_{ik} + {j{\overset{\_}{Q}}_{ik}}} \right)}} = 0};$

setting F(Y,P,Q,Û)=ε, J=ε^(T)·ε, where ε^(T) is a transposed vector of ε; substituting P+jQ={circumflex over (P)}+j{circumflex over (Q)}+G(β,{circumflex over (P)},{circumflex over (Q)}), minimizing J and determining Y and β;

-   -   a restoring unit (3), used for extracting an admittance matrix         of an element from Y and restoring element parameters including         resistance R, reactance X and susceptance B from the admittance         matrix of the element;     -   an output unit (4), used for outputting the element parameters         R, X, B and the power correction factor β.

The procedure of restoring element parameters from the admittance matrix Y is illustrated below in reference to several embodiments.

Embodiment 1: for an electric transmission line, whether short or long, all the equivalent circuits of the electric transmission line are as shown in FIG. 4. In FIG. 4, R is an equivalent resistance of the line, X is a power frequency equivalent reactance of the line, B is a power frequency equivalent susceptance of the line, and G is a power frequency equivalent conductance of the line.

$\begin{bmatrix} {\overset{.}{I}}_{1} \\ {\overset{.}{I}}_{1} \end{bmatrix} = {\begin{bmatrix} {\frac{1}{R + {jX}} + G + {jB}} & {- \frac{1}{R + {jX}}} \\ {- \frac{1}{R + {jX}}} & {\frac{1}{R + {jX}} + G + {jB}} \end{bmatrix} \cdot \begin{bmatrix} {\overset{.}{U}}_{1} \\ {\overset{.}{U}}_{2} \end{bmatrix}}$

So, if the element is an electric transmission line, the admittance matrix Y is:

$\begin{matrix} {{Y = \begin{bmatrix} {\frac{1}{R + {jX}} + G + {jB}} & {- \frac{1}{R + {jX}}} \\ {- \frac{1}{R + {jX}}} & {\frac{1}{R + {jX}} + G + {jB}} \end{bmatrix}},{U = \begin{bmatrix} U_{1} \\ U_{2} \end{bmatrix}},{P = \begin{bmatrix} P_{1} \\ P_{2} \end{bmatrix}},{Q = \begin{bmatrix} Q_{1} \\ Q_{2} \end{bmatrix}}} & {{Eq}.\mspace{14mu} 1} \end{matrix}$

The relationship between Y and the parameters R, X, B can be written out from Eq. 1:

$\begin{matrix} {{y_{11} = {\frac{1}{R + {jX}} + G + {jB}}},{y_{12} = {- \frac{1}{R + {jX}}}}} & {{Eq}.\mspace{14mu} 2} \end{matrix}$

After identifying Y, the parameters of the line can be obtained from Eq.2,

${{R + {jX}} = {- \frac{1}{y_{12}}}},{{G + {jB}} = {y_{11} + {y_{12}.}}}$

Embodiment 2: for a two-winding transformer, the admittance matrix Y can be written out according to the equivalent circuit of a two-winding transformer:

$\begin{matrix} {{Y = \begin{bmatrix} {{\frac{1}{R + {jX}} \cdot \frac{k}{k - 1}} + G + {jB}} & {- \frac{1}{\left( {R + {jX}} \right) \cdot k}} \\ {- \frac{1}{\left( {R + {jX}} \right) \cdot k}} & {\frac{1}{R + {jX}} \cdot \frac{k^{2}}{1 - k}} \end{bmatrix}},{U = \begin{bmatrix} U_{1} \\ U_{2} \end{bmatrix}},{P = \begin{bmatrix} P_{1} \\ P_{2} \end{bmatrix}},{Q = \begin{bmatrix} Q_{1} \\ Q_{2} \end{bmatrix}}} & {{Eq}.\mspace{14mu} 3} \end{matrix}$

-   -   where R is a copper resistance of a transformer, X is a         short-circuit reactance, G is an iron-loss conductivity, B is an         exciting susceptance, k is a non-standard ration of a         transformer, and k can also be identified.

Embodiment 3:for a three-winding transformer, referring to FIG. 5, R₁ is an equivalent resistance of winding 1, X₁is an equivalent reactance of winding 1, R₂ is an equivalent resistance of winding 2, X₂ is an equivalent reactance of winding 2, k₁₂ is a non-standard ratio of winding 1 and winding 2, R₃ is an equivalent resistance of winding 3, X₃ is an equivalent reactance of winding 3, k₁₃ is a non-standard ratio of winding 1 and winding 3, G is an iron-loss equivalent conductivity of the transformer, X_(m) is an equivalent exciting reactance of the transformer, so:

$\begin{matrix} {{Y = {Y_{11} + {Y_{12} \cdot Y_{22}^{- 1} \cdot Y_{21}}}},{U = \begin{bmatrix} U_{1} \\ U_{2} \\ U_{3} \end{bmatrix}},{P = \begin{bmatrix} P_{1} \\ P_{2} \\ P_{3} \end{bmatrix}},{Q = \begin{bmatrix} Q_{1} \\ Q_{2} \\ Q_{3} \end{bmatrix}}} & {{Eq}.\mspace{14mu} 4} \end{matrix}$

Where Y is an admittance matrix of the three-winding transformer, wherein:

$\begin{matrix} {{Y_{11} = \begin{bmatrix} \frac{1}{R + {jX}_{1}} & 0 & 0 \\ 0 & {\frac{1}{R_{2} + {jX}_{2}} \cdot \frac{k_{12}^{2}}{1 - k_{12}}} & 0 \\ 0 & 0 & {\frac{1}{R_{3} + {jX}_{3}} \cdot \frac{k_{13}^{2}}{1 - k_{13}}} \end{bmatrix}},{Y_{21} = \left\lbrack {{- \frac{1}{R_{1} + {jX}_{1}}}\mspace{14mu} - \frac{1}{\left( {R_{2} + {jX}_{2}} \right) \cdot k_{12}}\mspace{14mu} - \frac{1}{\left( {R_{3} + {jX}_{3}} \right) \cdot k_{13}}} \right\rbrack},{Y_{12} = Y_{21}^{T}},{Y_{22} = {\frac{1}{R_{1} + {jX}_{1}} + {\frac{1}{R_{2} + {jX}_{2}} \cdot \frac{k_{12}}{k_{12} - 1}} + {\frac{1}{R_{3} + {jX}_{3}} \cdot \frac{k_{13}}{k_{13} - 1}} + G + {\frac{1}{{jX}_{m}}.}}}} & {{Eq}.\mspace{14mu} 5} \end{matrix}$

Therefore, the admittance matrix Y of the three-winding transformer and the relationship between Y and the three-winding transformer parameters containing non-standard ratio can be obtained.

Embodiment 4: for a double-circuit parallel transmission line:

{dot over (U)} ₁₁ −{dot over (U)} ₁₂=(R ₁ +jX ₁)·(İ ₁₁ −{dot over (U)} ₁₁ ·jB ₁)+(R _(m) +jX _(m))·(İ ₂₁ −{dot over (U)} ₂₁ ·jB ₂)

{dot over (U)} ₂₁ −{dot over (U)} ₂₂=(R ₂ +jX ₂)·(İ ₂₁ −{dot over (U)} ₂₁ ·jB ₂)+(R _(m) +jX _(m))·(İ ₁₁ −{dot over (U)} ₁₁ ·jB ₁)

İ ₁₁ +İ ₁₂ ={dot over (U)} ₁₁ ·jB ₁ +{dot over (U)} ₁₂ ·jB ₁

İ ₂₁ +İ ₂₂ ={dot over (U)} ₂₁ ·jB ₂ +{dot over (U)} ₂₂ ·jB ₂

The formula of the double-circuit lines can be obtained after rewriting:

$\begin{matrix} {{Y = {\Gamma^{- 1} \cdot \Lambda}},{\Gamma = \begin{bmatrix} {R_{1} + {jX}_{1}} & 0 & {R_{m} + {jX}_{m}} & 0 \\ {R_{m} + {jX}_{m}} & 0 & {R_{2} + {jX}_{2}} & 0 \\ 1 & 1 & 0 & 0 \\ 0 & 0 & 1 & 1 \end{bmatrix}},{\Lambda = \begin{bmatrix} {1 + {\left( {R_{1} + {jX}_{1}} \right) \cdot {jB}_{1}}} & {- 1} & {\left( {R_{m} + {jX}_{m}} \right) \cdot {jB}_{2}} & 0 \\ {\left( {R_{m} + {jX}_{m}} \right) \cdot {jB}_{1}} & 0 & {1 + {\left( {R_{2} + {jX}_{2}} \right) \cdot {jB}_{2}}} & {- 1} \\ {jB}_{1} & {jB}_{1} & 0 & 0 \\ 0 & 0 & {jB}_{2} & {jB}_{2} \end{bmatrix}}} & {{Eq}.\mspace{14mu} 6} \end{matrix}$

where R₁, X_(i) and B₁ are a resistance, a reactance and a susceptance of line 1, andR₂, X₂ and B₂ are a resistance, a reactance and a susceptance of line 2, R_(m) and X_(m) are a mutual resistance and mutual reactance of the double-circuit lines.

Similarly, equations of a multiple-circuit parallel transmission line can be written out after considering the mutual impedance, thereby obtaining admittance matrixes and the relationship between the admittance matrixes and the parameters.

Embodiment 5: if identifying a line and a three-winding transformer:

${Y = \begin{bmatrix} Y_{11} & 0 \\ 0 & Y_{22} \end{bmatrix}},$

where Y₁₁ is a admittance matrix of the line, referring to Eq.1 for details; Y₂₂ is a admittance matrix of the three-winding transformer, referring to Eq.4 for details; P, Q and U column vector are also partitioned:

${P = \begin{bmatrix} P_{1} \\ P_{2} \end{bmatrix}},{Q = \begin{bmatrix} Q_{1} \\ Q_{2} \end{bmatrix}},{U = \begin{bmatrix} U_{1} \\ U_{2} \end{bmatrix}},$

where P₁, Q₁, U₁ are P, Q,U column vectors of the line, referring to Eq.1 for details; P₂, Q₂ and U₂ are P, Q, U column vectors of the three-winding transformer, referring to Eq.4 for details.

To identify multiple elements, the admittance matrixes of these elements are composed into diagonal elements of the partitioning matrixes, the off-diagonal elements are zero; correspondingly, P, Q, U column vectors can also be partitioned and arranged in order.

The identified power correction factor β in the present invention can be used for online correcting for an telemetering active power value and an telemetering reactive power value, the β obtained by identification has already reckoned in influences of current transformer (CT) errors, potential transformer (PT) errors and reactive measurement formula, so that it is not necessary to consider further the reactive measurement errors. Moreover, the present invention also identifies element parameters as well, and by substituting the element parameters into online application equations, under coaction of the power correction factor β and the element parameters, the pass rate of state estimation and application precision such asstability analysis, stability check and stability control, etc. can be improved. 

What is claimed is:
 1. A method for identifying an element parameter and a power correction factor of an electric power system, characterized in that, comprising the following steps: S1: inputting an active power telemetering steady state value {circumflex over (P)}, a reactive power telemetering steady state value {circumflex over (Q)}, and a voltage telemetering steady state value Û of a power grid with n elements, comprising: if n=1, inputting an active power telemetering steady state value {circumflex over (P)}_(c), a reactive power telemetering steady state value {circumflex over (Q)}_(c), and a voltage telemetering steady state value Û_(c) corresponding to the element; if n>1, inputting an active power telemetering steady state value {circumflex over (P)}_(c), a reactive power telemetering steady state value {circumflex over (Q)}_(c), and a voltage telemetering steady state value Û_(c) corresponding to each element, and inputting an active power telemetering steady state value {circumflex over (P)}_(i) and a reactive power telemetering steady state value {circumflex over (Q)}_(i) injected to a power grid node, where i=1,2, . . . ,N, and N is the number of the power grid nodes; S2: establishing a power correction equation P+jQ={circumflex over (P)}+j{circumflex over (Q)}+G(β,{circumflex over (P)},{circumflex over (Q)}) for a telemetering power, where G(β,{circumflex over (P)},{circumflex over (Q)}) is a power correction function regarding {circumflex over (P)} and {circumflex over (Q)}, β is a power correction factor, P is an active power telemetering correction value and Q is a reactive power telemetering correction value; S3: establishing a power voltage equation F(Y,P,Q,Û)=0, where Y is an admittance matrix related to said n elements; if n=1, said power voltage equation comprises a power voltage equation of an element; if n>1, said power voltage equation comprises a power voltage equation of an element and a power voltage equation of the power grid node; S4: setting F(Y,P,Q,Û)=ε, J=ε^(T)·ε, where ε^(T) is a transposed vector of ε; establishing simultaneous equations with P+jQ={circumflex over (P)}+j{circumflex over (Q)}+G(β{circumflex over (P)},{circumflex over (Q)}), minimizing J and determining Y and β; S5: restoring element parameters including resistance R, reactance X and susceptance B from Y; S6: outputting the element parameters R,X,B and the power correction factor β.
 2. The method according to claim 1, characterized in that: G(β,{circumflex over (P)},{circumflex over (Q)})=β_(p1)·{circumflex over (P)}+β_(p2)·{circumflex over (Q)}+β_(p0) +j(β_(q1)·{circumflex over (P)}+β _(q2)·{circumflex over (Q)}+β_(q0)), β={β_(p1), β_(p2), β_(p0), β_(q1), β_(q2), β_(q0)}.
 3. The method according to claim 1, characterized in that: G(β,{circumflex over (P)},{circumflex over (Q)})=β·({circumflex over (P)}+j{circumflex over (Q)}), β=β_(r)+jβ_(m).
 4. The method according to claim 1, characterized in that: said minimizing J and determining Y and β comprises conducting value-estimating for Y and β according to the theory of linear optimization or the theory of nonlinear optimization, so as to make J obtain a minimum value.
 5. The method according to claim 1, characterized in that: said active power telemetering steady state value {circumflex over (P)}, reactive power telemetering steady state value {circumflex over (Q)}, and voltage telemetering steady state value Û of a power grid with n elements are obtained according to the following steps: P1: inputting telemetering values of the electric power grid; P2: conducting steady state processing on the telemetering values, and obtaining telemetering steady state values; P3: selecting said active power telemetering steady state value {circumflex over (P)}, reactive power telemetering steady state value {circumflex over (Q)} and voltage telemetering steady state value Û of the power grid with n elements from the telemetering steady state values.
 6. The method according to any one of claims 1 to 5, characterized in that: for F(Y,P,Q,Û): if n=1, F(Y,P,Q,Û)=P_(c)+jQ _(c)−U_(c)·*({tilde over (Y)}·Ũ_(c)), where Y is an admittance matrix of an element; if n>1, ${F\left( {Y,\overset{\_}{P},\overset{\_}{Q},\hat{U}} \right)} = \left\{ \begin{matrix} {{\overset{\_}{P}}_{c} + {j{\overset{\_}{Q}}_{c}} - {{\hat{U}}_{c} \cdot^{*}\left( {\overset{\sim}{Y} \cdot {\overset{\sim}{U}}_{c}} \right)}} & {{power}\mspace{14mu} {voltage}\mspace{14mu} {equation}\mspace{14mu} {of}\mspace{14mu} {element}} \\ {{{\overset{\_}{P}}_{i} + {j{\overset{\_}{Q}}_{i}} - {\sum\limits_{k = 1}^{n_{i}}\; \left( {{\overset{\_}{P}}_{ik} + {j{\overset{\_}{Q}}_{ik}}} \right)}},{i = 1},2,\ldots,N,} & {{power}\mspace{14mu} {voltage}\mspace{14mu} {equation}\mspace{14mu} {of}\mspace{14mu} {power}\mspace{14mu} {grid}\mspace{14mu} {node}} \end{matrix} \right.$ where Y is an admittance matrix related to n elements, {tilde over (Y)} is a conjugate matrix of Y, Ũ_(c) is a conjugation of Û_(c), “·*” stands for multiplying the corresponding items; n_(i) is the number of elements connected to node i, P _(ik) is an active power telemetering correction value of element k connected to node i, Q _(ik) is a reactive power telemetering correction value of element k connected to node i.
 7. A system for identifying an element parameter and a power correction factor of an electric power system, characterized in that, comprising the following units: a steady state value input unit, used for inputting an active power telemetering steady state value {circumflex over (P)}, a reactive power telemetering steady state value {circumflex over (Q)} and a voltage telemetering steady state value Û of a power grid with n elements, comprising: if n=1, inputting an active power telemetering steady state value {circumflex over (P)}_(c), a reactive power telemetering steady state value {circumflex over (Q)}_(c) and a voltage telemetering steady state value Û_(c) corresponding to the element; if n>1, inputting an active power telemetering steady state value {circumflex over (P)}_(c), a reactive power telemetering steady state value {circumflex over (Q)}_(c) and a voltage telemetering steady state value Û_(c) corresponding to each element, and inputting an active power telemetering steady state value {circumflex over (P)}_(i) and a reactive power telemetering steady state value {circumflex over (Q)}_(i) injected to a power grid node, where i=1,2, . . . ,N, and N is the number of the power grid nodes; a minimal calculating unit, used for establishing a power correction equation P+jQ={circumflex over (P)}+j{circumflex over (Q)}+G(β,{circumflex over (P)},{circumflex over (Q)}) for a telemetering power, where G(β,{circumflex over (P)},{circumflex over (Q)}) is a power correction function regarding {circumflex over (P)} and {circumflex over (Q)}, β is a power correction factor, P is an active power telemetering correction value and Q is a reactive power telemetering correction value; establishing a power voltage equation F(Y,P,Q,Û)=0, where Y is an admittance matrix related to said n elements; if n=1, said power voltage equation comprises a power voltage equation of an element; if n>1, said power voltage equation comprises a power voltage equation of an element and a power voltage equation of the power grid; setting F(Y,P,Q,Û)=ε, J=ε^(T)·ε, where ε^(T) is a transposed vector of ε; establishing simultaneous equations with P+jQ={circumflex over (P)}+j{circumflex over (Q)}+G(β,{circumflex over (P)},{circumflex over (Q)}), minimizing J and determining Y and β; a restoring unit, used for restoring element parameters including resistance R, reactance X and susceptance B from Y; an output unit, used for outputting the element parameters R,X,B and the power correction factor β.
 8. The system according to claim 7, characterized in that: G(β,{circumflex over (P)},{circumflex over (Q)})=β_(p1) ·{circumflex over (P)}+β_(p2) ·{circumflex over (Q)}+β_(p0) +j(β_(q1) ·{circumflex over (P)}+β_(q2) ·{circumflex over (Q)}+β _(q0)), β={β_(p1), β_(p2), β_(p0), β_(q1), β_(q2), β_(q0)}.
 9. The system according to claim 7, characterized in that: G(β,{circumflex over (P)},{circumflex over (Q)})=β({circumflex over (P)}+j{circumflex over (Q)}), β=β_(r) +jβ _(m).
 10. The system according to claim 7, characterized in, further comprising a steady-state value acquisition unit, and said steady-state value acquisition unit comprises: a steady-state processing module, used for conducting steady-state processing on telemetering values of the electric power system and obtaining a telemetering steady state values; a steady-state value selection module, used for selecting said active power telemetering steady state value {circumflex over (P)}, reactive power telemetering steady state value {circumflex over (Q)} and voltage telemetering state value U of the power grid with n elements from the telemetering steady state values.
 11. The system according to any one of claims 7 to 10, characterized in that: for F(Y,P,Q,Û): if n=1, F(Y,P,Q,Û)=P _(c)+jQ _(c)−Û_(c)·*({tilde over (Y)}·Ũ_(c)), where Y is an admittance matrix of an element; if n>1, ${F\left( {Y,\overset{\_}{P},\overset{\_}{Q},\hat{U}} \right)} = \left\{ \begin{matrix} {{\overset{\_}{P}}_{c} + {j{\overset{\_}{Q}}_{c}} - {{\hat{U}}_{c} \cdot^{*}\left( {\overset{\sim}{Y} \cdot {\overset{\sim}{U}}_{c}} \right)}} & {{power}\mspace{14mu} {voltage}\mspace{14mu} {equation}\mspace{14mu} {of}\mspace{14mu} {element}} \\ {{{\overset{\_}{P}}_{i} + {j{\overset{\_}{Q}}_{i}} - {\sum\limits_{k = 1}^{n_{i}}\; \left( {{\overset{\_}{P}}_{ik} + {j{\overset{\_}{Q}}_{ik}}} \right)}},{i = 1},2,\ldots,N,} & {{power}\mspace{14mu} {voltage}\mspace{14mu} {equation}\mspace{14mu} {of}\mspace{14mu} {power}\mspace{14mu} {grid}\mspace{14mu} {node}} \end{matrix} \right.$ where Y is an admittance matrix related to n elements, {tilde over (Y)} is a conjugate matrix of Y, Ũ_(c) is a conjugation of Û_(c), “·*” stands for multiplying the corresponding items; n_(i) is the number of elements connected to node i, P _(ik) is an active power telemetering correction value of element k connected to node i, and Q _(ik) is a reactive power telemetering correction value of element k connected to node i. 